In many applications, the rotational speed, position, or angle of a shaft or other rotating component is determined using magnetic field sensors. For example, Hall sensors or magnetoresistive sensors (such as GMR, AMR, TMR, etc.) can be arranged on or adjacent to the rotating component. In off-axis sensing, the rotating component includes a magnetic multipole that has permanently magnetized portions, such that as the rotating component rotates a sensor positioned off of the rotational axis observes fluctuations in the magnetic field strength and/or direction.
There are many possible axial orientations of the sensor in an off-axis system. In general, one edge of a sensor die is kept parallel to the rotational axis of the rotating component. More particularly, two primary orientations are most commonly used for cylindrical, rotating components such as cam-shafts. In the first, the surface of the die is tangential to a cylindrical surface (where the axis of the cylinder coincides with the rotational axis). In the second, the surface of the die is perpendicular to the cylindrical surface. The magnetic target can be a diametrically magnetized component that is mounted on the rotating component, either at a point along the length of the component or else at an end of the component. Conventional systems measure the absolute rotational position of the rotating component by measuring the magnetic field caused by the multipole at each of several locations.
In similar conventional systems, linear position can also be ascertained using multiple sensor dies arranged along a linearly moving magnetic target.